The primary objective of this program involves the development of a clinically useful, reliable, and safe test to measure the severity of atherosclerosis. This will be accomplished by the testing, in animals, of radioactive lipophilic dye which when injected intra-arterially, and retained for 3 minutes between tourniquets, will give a washout curve indicative of the lipid content and extent of atherosclerosis of the artery wall. Eventual human application would follow suitable systemic and local toxicity tests. A Toluene-azo-naphthol (TAN) organic dye has been synthesized, tagged with I-125 and purified, and the final product has been tested by several methods for chemical and radio purity characteristics as well as lipophilicity and radiopharmaceutical properties. Preliminary retention and excretion studies in rats have been completed. Washout curves of abdominal aortas in normal and atherosclerotic living rabbits have just begun with the availability of the dye. Concurrently, we are attempting to anatomically locate "compartments" or layers of artery wall having different washout rates.